Pressure contact



June 30, 1953 c, J, ADAMS 2,644,145

PRESSURE CONTACT Y Filed June 2'7 1950 JkMe/ZZZW: Jaw/Z65 Madam/(,5

Patented June 30, 1953 PRESSURE CONTACT Charles J. Adams, Park Ridge, 111., assignor to American Phenolic Corporation, Chicago, 111., a corporation of Illinois Application June 27, 1950, Serial No.'170,577

8 Claims.

This invention relates to contacts for electrical connectors, and particularly to the type of contacts generally designated as pressure contacts. Such contacts are distinguished from the various sleeve and pin types in that their mating parts are arranged in abutting relationship, rather than designed to telescope Within each other. Ordinarily, they are provided with one spring-urged contact, which is held in abutting relationship With a fixed contact of the mating connector.

Itis the primary object of the present invention to provide a pressure contact assembly including an internal spring, yet so designed that no appreciable electrical current flows through the spring itself. A further object is to provide such a contact wherein all parts of the contact are united in a self-contained unitary assembly.

The accomplishment of these objects is of advantage in several ways. For one thing, it provides a contact of unusually low resistance, since the inherent resistance of the spring does not contribute to the milli-volt drop across the connector. More important, however, is the fact that by this expedient, physical deterioration of the spring is avoided,so that it maintains full strength and resiliency indefinitely, and is not subject to the rapid physical deterioration that occurs if any appreciable current flows through the spring. This deterioration is believed to be primarily due to the fact that since the cross sectional area of a contact spring is almost always a very small fraction of the total cross sectional area of the contact, any overload (even the momentary overloads to which contacts of these types are often subjected in normal use), will cause sufficient heat to be developed in the spring at the instant of such an overload to reduce or destroy the temper of the metal. that even if the current flowing through the spring does not exceed the normal contact ratin the long continued electron flow through a tempered spring results in a physical change sufiicient to weaken it appreciably. Obviously, either of these effects reduces the effectiveness of the e contact which has a self-contained internal spring, yet is of inherently lower resistance and of more constant resistance than those heretofore devised. g

In addition to the above, the provision of a contact in which the current does not flow through the spring permits the spring to be Italso appears formed of a metal chosen solely because of deslrable mechanical characteristics, irrespective'of its electrical properties. Also, it avoids unwanted inductive effects in the contact. Such effects are present to a certain extent in any spring, and more particularly noticeable in connection with springs of the conventional helical coil type.

. A further object of the invention is to provide a pressure contact including a plunger mounted for sliding movement in a tubular housing, with a coil spring within the housing and acting on the plunger so that it performs a dou ble function; that is, so that the spring urges the contact plunger outwardly and holds it in abutting relation with the coacting contact of a mating connector, and at the same time urges the inner end of the plunger laterally, so that it is held in firm electrical contact with the sleeve in which it slides.

It is a further object of the invention to provide a pressure contact including an internal spring, wherein the parts are so designed as to prevent the flow of an appreciable current through said spring, yet wherein this object is accomplished by short circuiting the spring by an electrical path of far less resistance than is inherent in the spring itself, rather than by insulting the spring. This is of advantage in that it not only reduces the cost of manufacture, but also in that it avoids any need of insulating material within the contact assembly, and thus simplifies the physical structure of the connector.

The foregoing objects are accomplished according to the present invention by providing, in an electrical connector, a self-contained unitary contact assembly comprising a housing in the form of a tubular sleeve and spring-urged plunger, with the plunger sl-idable in the housing and having a contact button extending from the end thereof. The contact is urged outwardly from the housing by a simple coil spring, but the inner end of the plunger is provided with an inclined cam surface. A ball is inserted between the spring and the cam, so that the spring acts through the ball to impose a lateral thrust on the contact plunger and hold iti n secure electrical engagement with the inside wall of the housing.

A preferred embodiment of the invention is illustrated in the drawings hereof, wherein:

Figure 1 is a side elevational view of an ele'ctrical connector fitting, being shown partially in.

section'to illustrate a preferred application of a pressure contact constructed in accordance with the present teachings; and

Figure 2 is a central sectional view of a pressure contact as contemplated bythis invention. A contact of the type here disclosed may be employed in many and various types of connec tors, but, as shown in Figure l, the contact'assembly, generally designated as I I has a neck portion I l and a pai of flanges l2 and I3 molded in a dielectric insert M, with a body or housing portion T5 of the contact extending forwardly through a dielectric insert l3. These inserts are both mounted in a metal connector fittin l1, and may be held in position therein by any convenient means, as by the spring retainer ring l8 and shoulder [9. The inner end of the contact assembly It may be provided with a hollow end terminal section 21 cut away at 22 to provide an easily accessible soldering cup to which a flexible conductor may be secured.

The housing or body portion 15 of the contact assembly has an internal bore 24 in which the contact plunger 25 is mounted. The plunger 25 has a contact button 26 at its extreme outer end and is provided with reduced neck portions 21 and 28. The outer end of the tubular housing [5 is spun over to form an inwardly extending flange 31 extending into the neck portion 21, so that the outward movement of the plunger is limited by the engagement of the flange 3i and the shoulder 32, while inward movement of the plungeris limited by engagement of the flange 31 with the shoulder 33. As shown, the connector is provided with a resilient rubber seal 34, which closely surrounds the neck 2'! to exclude moisture from the internal parts of the assembly.

The inner end of the plunger 25 is cut diagonally to form an oblique or mitered cam surface 38. A helical coil spring 36 and ball 31 are positioned in the bore 24. Thus, the longitudinal force exerted by the spring 36 acts through the ball 31 and against the cam surface 38 f the plunger to urge the plunger outwardly, but also to urge the inner end of the plunger laterally into intimate wiping contact with the inside of the bore 24 at the point 39. This faoe'of the plunger is slightly rounded at 40 to insure smooth sliding action and maintain a low resistance electrical contact without any tendency to scratch the internal surfaces of the bore 24.

For the fullest accomplishment of the aims of the present invention, it is desirable that the current carrying parts, that is, the outer housing (from the terminal 2 I, through the neck I I, the flanges l 2I3, and the tubular portion l) be of metal having low electrical resistance, and that the entire plunger (from the inner surface 40 to the button 26) be formed of metal having equally low resistance properties. It is unnecessary, however, that low resistance metals be used for the spring 36 or for the ball 31, and it follows that these materials may be selected solely on the basis of their mechanical properties. That is, they may be chosen from materials having the desired characteristics of resiliency, resistance to corrosion, etc., irrespective of their electrical properties.

In any event, it will be seen that when the contact is in use there will be no appreciable flow of current through the spring 36 and the ball 31. This is for the reason that the resistance through the wiping contact at the point 39 and then through the plunger 25, will be an extremely small fraction of resistance presented by the path through the spring 36 and ball 31. Thi is true even if the metal of the same electrical conductivity is used for all of these parts, since elec trical resistance is directly proportional to the length of a conductor and inversely proportional to its cross-sectional area. Obviously, the path through the spring is of high resistance, being a long path with very small cross sectional area;

the path through the plunger and the cylindrical walls of the connector, on the other hand, is short and of relatively great area. The effect is even greater when relatively high resistance metals are employed for the spring and ball of the unit. Thus, as a matter of actual practice, it is of advantage to make the contact housing and plunger of copper, and to use a metal such as stainless steel for the ball and spring.

From examination of Figure 2, it will be readily apparent that the electrical path through the spring 36 is many times longer and yet of far less cross section than the electrical path through the tubes surrounding it. It follows then that if a low resistance contact is established between the plunger and the sleeve, the current flow through the unit will be almost entirely through these pieces rather than through the spring itself. According to the present teachings, the resistance between the plunger and sleeve is reduced to a negligible value by the provision of the cam surface 38, which acts laterally on the inner end of the plunger and holds the plunger and sleeve in firm contact at 39, so as to effectively short circuit any possible path of current flow through the spring itself.

With this arrangement, the plunger may be machined with adequate tolerances, and with enough clearance so that it is free to move in and out easily, yet it will be held in firm electrical contact with the sleeve at all times. In short, it is a construction which allows the plunger moving in the tube to be quite loose mechanically, yet firm electrically, so that free inward and outward movement may be accomplished Without sacrifice of electrical conductivity between the two parts.

From the foregoing, it is believed clear-that by the teachings of the present disclosure the objects of the present invention are accomplished and a structure provided wherein the internal spring of the unit will not be subject to deterioration due to heat developed by current flowing through it or to the deteriorating effects of long continued electron flow. This is because the sprin is effectively short-circuited by contact between the members l5 and 25 at the point 39.

It is generally believed that there is an electrical resistance at points of contact. This is erroneous, however, due to the fact that if the point of contact is looked at as a conductor, its resistance is directly proportional to its length and inversely proportional to its area. Therefore, if points of contact havin an area of one unit and a length of zero units, and the resistance any value whatsoever, then the resistance of the points of contact would be 1 0/1 resistance=0 There is an apparent resistance, however, which is due to the material used in making con tact which would follow the'inversesquare law. If a material could be found with zero resistance (infinite conductivity) regardless of how small the point of contact became as long as it did not have length, contact and contact body resistance would be zero. Thus, with low resistance metals such as copper or silver, the resistance at the point 39 is so small that no appreciable current flows through the spring 36. The same applies as to the contact between the convex button 26 and the contacts of the mating connector. 1

It follows that a connector contact according to these teachings will retain its original efficiency over an indefinite period and will not be subject to damage as a result of moderate overload. Moreover, it avoids unnecessary inductive effects such as arise in structures wherein any substantial proportion of the current carried by the contact flows through the spring.

In addition to the above, the arrangement of parts in this contact is of advantage in that the mounting shank l I and solder cup 22 are in fixed relationship to the housing and other parts. Thus, even if a severe strain is placed on the contact, it cannot pull the convex head portion 26 away from its mating contact.

Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. In an electrical connector, a pressure contact comprising a tubular housing with a plunger therein, the plunger including a slide portion Within the tubular housing and a contact portion extending outwardly from one end thereof; a coil spring within the tubular housing uring said plunger longitudinally outwardly from said housing, together with means to press an inner portion of said plunger laterally against the inside surfaces of said housing; said means comprising an angular face portion on the inner end of the plunger, and a ball interposed between the end of the coil spring and said angular face portion.

2. In an electrical connector, a pressure contact comprising a tubular housing with a plunger therein, the plunger including a slide portion within the tubular housing and a contact portion extending outwardly from one end thereof; a coil spring within the tubular housing urging said plunger longitudinally outwardly from said housing, together with means to limit the outward movement of the plunger and hold said plunger and housing in assembled relationship, and means to press an inner portion of said plunger laterally against the inside surfaces of said housing; said means comprising an angular face portion on the inner end of the plunger, and a ball interposed between the end of the coil spring and said angular face portion.

3. In an electrical connector, a pressure contact comprising a tubular housing with a plunger therein, the plunger including a slide portion within the tubular housing and a contact portion extending outwardly from one end thereof; a coil spring within the tubular housing urging said plunger longitudinally outwardly from said housing, together with a shiftable operating member actuated by said coil spring and located at the inner end of the plunger to press an inner portion of said plunger laterally against the inside surfaces of said housing.

4. In an electrical connector, a pressure contact comprising a tubular housing with a plunger therein, the plunger including a slide portion portion of said plunger laterally against the inside surfaces of the housing to maintain a low surface within the connector and a pressure contact comprising a plunger including a slide portion engaging said conducting surface and a contact portion extending outwardly from the connector; together with spring means urging said plunger longitudinally outwardly from said connector and means at the inner end of the plunger to exert a lateral thrust on the slide portion of said plunger; said means comprising a cam surface.

6. In an electrical connector, a conducting surface within the connector and a pressure contact comprising a plunger including a slide portion engaging said conducting surface and a contact portion extending outwardly from the connector; together with'a coil spring within the connector urging said plunger longitudinally outwardly from said connector and an intermediate member at the inner end of, the plunger and operatively interconnecting said coil spring and plunger to exert a lateral thrust on the slide portion of said plunger in response to longitudinal force exerted by said coil spring.

7. In an electrical connector, 9. fixed conducting surface within the connector and a pressure contact comprising a plunger in sliding engagement with said conducting surface and having a contact portion extending outwardly from the connector, spring means urging said plunger longitudinally outwardly, together with means to press an inner portion of said plunger against said conducting surface; said means comprising an angular face portion on the inner end of the plunger, and a ball interposed between the end of the spring and said angular face portion.

8. In an electrical connector, a fixed conducting surface within the connector and a pressure contact comprising a plunger in sliding engagement with said conducting surface and having a contact portion extending outwardly from the connector, spring means urging said plunger longitudinally outwardly, together with means at the inner end of the plunger to press an inner portion of said plunger against said conducting surface.

CHARLES J. ADAMS.

References Cited in the file of this patent UNITED STATES PATENTS Number Nam-e Date 1,605,904 Van Brunt Nov. 2, 1926 2,425,802 Harris et a1 Aug. 19, 1947 FOREIGN PATENTS Number Country Date 1 283,309 England Jan. 12, 1928 

